Measurements of Low Frequency Noise of Infrared Photo-Detectors with Transimpedance Detection System

The paper presents the method and results of low-frequency noise measurements of modern mid-wavelength infrared photodetectors. A type-II InAs/GaSb superlattice based detector with nBn barrier architecture is compared with a high operating temperature (HOT) heterojunction HgCdTe detector. All experiments were made in the range 1 Hz - 10 kHz at various temperatures by using a transimpedance detection system, which is examined in detail. The power spectral density of the nBn’s dark current noise includes Lorentzians with different time constants while the HgCdTe photodiode has more uniform 1/f - shaped spectra. For small bias, the low-frequency noise power spectra of both devices were found to scale linearly with bias voltage squared and were connected with the fluctuations of the leakage resistance. Leakage resistance noise defines the lower noise limit of a photodetector. Other dark current components give raise to the increase of low-frequency noise above this limit. For the same voltage biasing devices, the absolute noise power densities at 1 Hz in nBn are 1 to 2 orders of magnitude lower than in a MCT HgCdTe detector. In spite of this, low-frequency performance of the HgCdTe detector at ~ 230K is still better than that of InAs/GaSb superlattice nBn detector

Multi-technique characterisation of InAs-on-GaAs wafers with circular defect pattern

The article presents the results of diameter mapping for circular-symmetric disturbance of homogeneity of epitaxially grown InAs (100) layers on GaAs substrates. The set of acceptors (beryllium) doped InAs epilayers was studied in order to evaluate the impact of Be doping on the 2-inch InAs-on-GaAs wafers quality. During the initial identification of size and shape of the circular pattern, non-destructive optical techniques were used, showing a 100% difference in average roughness between the wafer centre and its outer part. On the other hand, no volumetric (bulk) differences are detectable using Raman spectroscopy and highresolution X-ray diffraction. The correlation between Be doping level and circular defect pattern surface area has been found